There is known an excavator including a position detection device to detect the current position of a working point of a working machine. For example, at the excavator disclosed in Patent Literature 1, the position coordinates of a blade edge of a bucket are computed based on position information from GPS antennas. Specifically, the position coordinates of the blade edge of the bucket are computed based on parameters such as positional relationship between the GPS antennas and a boom pin, respective lengths of a boom, an arm, and a bucket, respective direction angles of the boom, the arm, and the bucket, and others.